Electron beam device



Filed July 29. 1958 Fig.|.

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WITNESSES: INVENTOR: RMQEQR George C. Sz|klq| fsgazatss Fatented Feb. 5, 1962 it s than

3,020,438 ELEtZTRON BEAM DEVICE George C. Sziklai, Princeton, N..ll., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed July 29, 1953, Ser. No. 751,659 Claims. (Cl. 315-1) This invention relates to electron beam devices and, more particularly, to electron beam devices including a semiconductor target member having a plurality of semiconductor transition regions. The term transition region used in this application refers to the region 'between two homogeneous semiconductor regions, in which the impurity concentration changes and includes PN junctions, IN junctions, IP junctions, NN junctions and PP junctions.

Recently there have been attempts to obtain better performance from receiving tubes and small power tubes, but because of the basic spatial and alignment limitations in conventional electron tube structures, further increases in what is known as the trans-conductance-to-plate current ratio have been of a minor nature.

This transconductance is defined by the expression TAE,

where G is the transconductance in ampere/volt or mhos, I is the plate current in amperes and E is the grid voltage in volts. In conventional tubes, G is defined as the slope of the plate current vs. the grid voltage curves at the operating point.

One departure from conventional electronic tube design which has shown promise for overcoming these basic limitations is the beam deflection tube, such as that disclosedin an article entitled Beam Deflection Control for Amplifier Tubes, by G. R. Kilgore, which appeared in the RCA Review of September 1947, p. 480 ff., and also an'article by E. W. Herold and C. W. Mueller, entitled Beam-Deflection Mixer Tubes for UHF, which appeared in theMay 1949 issue of Electronics, pages 76 through 80. I

In general, a beam deflection tube includes an electron gun for generating an electron sheet beam, a pair of deflection plates for deflecting the electron beam and a target or anode upon which the electron beam impinges. An interceptor, usually a plate or a wire, is positioned between the deflection plates and the anode so that when the beam is deflected in a certain manner, part or all of the electron beam will strike the interceptor and not the anode.

' In beam deflection tubes with an electron beam of uniform density, we may consider A1,, Gm- AE where E is the deflection plate voltage which will defleet the electronbeam at the interceptor by a distance equal to the beam thickness and I is the maximum plate current which is obtained when the beam is completely on the anode.

Beam deflection tubes provide (1) approximately 20 times the transconductance-to-plate current ratio available with the conventional grid control tubes, (2) much greater gain-bandwidth product due to the lower interelectrode capacitance and higher mutual conductance, (3) better signal to noise ratios than those obtained with conventional tubes due to the higher input impedance and higher ratio of transconductance to beam current, and also (4) materially reduce the local oscillator radiation due to' improved isolation of the input electrodes. Also,

(5') the transit time problem is reduced which makes improved UHF amplifiers and mixers possible. However, one drawback of these tubes is the fact that the maximum plate current obtainable is usually less than one milliampere which therefore prevented reaching a high transconductance. In order to overcome this, tubes were made including secondary emission electron multipliers. These tubes, while providing transconductance values as high as 50,000 micrornhos, had a disappointingly short life.

My invention overcomes these difliculties by providing a suitable semiconductor target upon portions of which the electron beam of a beam deflection tube will impinge, thereby radically increasing the power output of the tube because of an extremely lar e current gain factor. Accordingly, it is an object of my invention to provide an improved electronic current multiplier.

It is another object of my invention to provide an improved electron beam tube having a suitable semi-conductor target member.

It is a further object to provide an improved electron beam deflection device having a semiconductor target member including a plurality of semiconductor transition regions.

; It is an additional object to provide an improved elec-- tron beam deflection device having a transistor as a target member. These and other objects of this invention will be apparent from the following description taken in accordance with the accompanying drawing, throughout which like reference characters indicate like parts, which drawing forms a part of this application, and in which: 7

FIGURE 1 is a sectional view and circuit diagram of an electron beam device in accordance with one embodiment of my invention; p FIG. 2 is a sectional view and circuit diagram of an electron beam deflection device in accordance with another embodiment of my invention; and

FIG. 3 is a side sectional view of asemi-conductor target member for an electron beam deflection device in accordance with another embodiment of my invention. In FIG. 1, there is shown an electron beam device which includes a semiconductor target member 19 in the form of a PNP junction transistor. An envelope 11 made of a suitable material, such as glass, encloses the target member 19 and a suitable electron beam generating means 13 which generates an electron beam 15 of a desired configuration. The electron beam 15 ordinarily is in the form of a thin sheet of electrons, but if desirable, the electron beam 15 may be in other forms, such as a spotwhich, however, may provide lower current. The electron beam 15 passes between deflection plates 17, to which suitable voltages may be applied, and finally impinges upon the target member 19. It is frequently desirable to utilize an intercepter 33 which is shown in the form of a wire-like member, but which may also be in other forms, such as a plate. This interceptor 33 will intercept part'of the electron beam 15 if the electron beam 15 is deflected by the deflection plates 17 in a downward direction, thus allowing only certain portions of the electron beam 15 to impinge upon the target member 19. It also may be desirable to provide a suppressor 31 adjacent the target member to intercept any,

secondary electron emission from the anode. The beam intensity may also be controlled by additional grids which, if desired, may be placed between the electron beam generating means 13 and the deflection plates 17.

The semiconductor target member 19 shown in this particular embodiment may be in the form of a junction transistor. A suitable junction transistor may be in the form of an PNP transistor which may include an emitter.

21 made of semiconductor material having P-type conductivity, a collector 23 made of semiconductor material also having P-type conductivity, and a thin base region 25 positioned between the emitter 21 and the collector 23 and made of a semiconductor material having N-type conductivity. Between the P-type emitter 21 and the N type base region 25, there is a semiconductor transition region of the type known as a PN junction, and is referred to as the emitter-base PN junction 27. Also between the collector 23 and the base region 25, there is another semiconductor transition region of the PN junction type herein referred to as the collector-base PN junction 29.

In the particular embodiment shown in FIG. 1, the emitter 21 is connected to the output and to the load 37, and as shown by the circuit diagram, the collector 23 is connected to the positive pole of a potenial source 39, and the negative pole of a similar potential source 39 is also connected to the electron beam generating means 13.

In a conventional junction transistor not associated with a beam deflection device as in FIG. 1, current amplification may be produced by the use of adequate circuitry. For example, when a P-type emitter is connected to the negative pole of a first potential source and a P-type collector is connected to the positive pole of a second potential source and the base region is connected to the opposite pole of the above-mentioned potential sources, a change in the bias voltage at the emitter will change the charge distribution and potential conditions in. the base region so that the impedance is modified. This modified impedance is reflected in a change of current through the transistor between the collector and the emitter at a given collector voltage. However, it has been found in dealing with transistors, that the maximum frequency at which they will operate is a function, among other things, of the thickness of the base layer. As this thickness decreases, the maximum operating frequency increases. Therefore, it can be seen that it is desirable to make the transistor with a base layer of minimum thickness. However, in the conventional transistor, if the base layer is very thin, it becomes very difficult to make a lead connection to the base region without causing a short across the base region. In my invention, the electron beam 15 provides this electrical contact to the thin base region 25. This arrangement has the advantage of providing a connection which will not permit a short even if the beam is thicker than the base region 25 because of the discrete nature of the electrons.

In accordance with my invention, when the electron beam 15 bombards the target member 19, an induced conductivity is observed. conductivity can be at least partially attributed to the production of internal secondary electrons by the primary electrons of the impinging electron beam 15. The secondary electrons are probably formed because the primary electrons lose energy as they pass into the target material, which energy may be used to raise electrons from the valence to the conduction band, thereby providing additional current carriers. Also, the conductivity may be increased by the production of holes" which in effect result from the removal of electrons from the valence band to the conductive band. Also, the primary electrons from the beam itself attribute to the induced conductivity. In other words, the electron beam not only charges the material with the primary electrons from the beam itself, but also produces electron-hole pairs. The number of such pairs per incident electron is proportional to the electron energy and is found by dividing the voltage of the impinging electron beam by approximately 3.5. These electron-hole pairs, when produced in the base region of a transistor, act exactly as though the increased minority carrier concentration was produced in ordinary transistor emitter action. Therefore, it can be seen that the gain resulting from the transistor action because of the impinging electron beam is related to the electron-hole pair density rather than It is believed that this induced the density of electrons from the beam itself. These two amplification factors, namely, the transisor amplification and the electron beam multiplication, act independently, and their productis the gain of the electron beam device. With a device such as that shown in FIG. 1 a tremendous current gain may be obtained, and a transconductance on the order of 120,000,000 micromhos results. While this transconductance may be larger than is necessary for most applications at present, it does indicate the magnitude of the tremendous advantage that can be obtained by combining a transistor with a medium high velocity electron beam.

Of course, the target member 19 is not restricted to a PNP junction transistor of the type shown. NPN, NPIN, PNIP or other devices having a plurality of semiconductor transistor regions may also be used in a similar maner. In general, the target member must have a plurality of semiconductor transition regions and be capable of current gain due to transistor action in cooperation with the impinging electron beam.

A target member 19 similar to that shown in FIG. 1 may be made of any suitable semiconductor material such as germanium or silicon or some suitable semiconductor compound such as indium arsenide. However, because the entire device may be subject to a high temperature bake-out during manufacture, a silicon semiconductor device may be preferable. Suitable silicon transistors may be made by the processes known as double doping, rate growing, alloying or fusion, diffusion or by other suitable processes depending on the particular configuration, characteristics, etc., desired. These methods are described in general in Section 7, entitled Methods of Preparing P-N Junctions, by W. C. Dunlap, Jr., in the Handbook of Semiconductor Electronics, edited by Lloyd I. Hunter, published by McGraw-Hill Book Company, 1956, First Edition.

For example, suitable silicon NPN transistors may be made by the double doping process using boron as the P-type doping material and arsenic as the N-type doping material. As a single crystal of silicon is grown, the melt from which it is grown, or pulled, is doped with the proper amounts of the desired impurities as is known in the art. The crystal is rotated and the melt is stirred to insure even distribution of the impurity. Also the temperature must be accurately controlled.

First, the melt is doped with a suitable donor impurity such as arsenic, to provide a high resistivity (about 5 ohms/cm. N-type collector regon. Then the melt is doped with a sufficient quantity of a suitable acceptor impurity, such as boron, to provide a medium-resistivity (about 1 ohm/cm.) P-type base region. After the crystal has grown about 0.001 to 0.01 mm., the melt is doped with a suitable donor impurity, such as arsenic, to provide a low resistivity (about 0.5 ohm/cmfi) emitter. Either the single reservoir or the split reservoir method may be used. Of course, other suitable donor and acceptor impurities may be used depending on the intrinsic semiconductor materials used, and the characteristics desired. For example, suitable donor materials, in addition to arsenic, include antimony, phosphorus and bismuth. Suitable acceptor materials, in addition to boron, include gallium, indium, aluminum and tellurium.

In the particular embodiment shown in FIG. 1, a suit able thickness for the base region 25 is approximately 0.005 mm., with the thickness of the emitter- 21 being about 1 mm., and the collector 23 being about 1 mm. The thickness of the target member 19 itself from front to back may be on the order of 1 mm., and the overall is positioned a base region .47 having a collector-base transition region 51 and an emitter-base transition region 49. The emitter is connected to the output and the load 37, whilethe collector is connected to the positive pole of a potential source 39. In a particular embodiment shown an NPN device is utilized but as in the case with FIG. 1, other multi-transition region devices may be used.

As can be seen in FIG. 2, the transition regions or junctions are substantially perpendicular to the direction of the electron beam 15, whereas in FIG. 1, these junctions were substantially parallel to the direction of the electron beam 15. To allow the electron beam to impinge upon the base region 47, an aperture 53 is formed'in the emitter 43. This has the advantage that the electron injection from the electron beam 15 may be made very close to the conducting zone of the transistor which permits high frequency operation and also provides for improved heat dissipation. The emitter 43 can be made very thin; for example, on the order of 1 mm. 'or less, and also serves as an interceptor edge and as a heat sink for the portion of the base region 47 which is in intermediate contact with the emitter 43. It can be seen that .FIG. 2 does not include an interceptor similar to the interceptor 33 shown in FIG. 1. Suitable dimensions for the target member 4-1 include base region 47 thickphorus pentoxide may be diffused into N-type silicon.

The gallium will diffuse ahead to form the P-type base region 47 and the phosphorus will trail the gallium and form the N-type emitter 43.; The aperture 53 may be formed by suitable grinding or etching to expose the base region 47. Heat dissipating metallic members may then be attached to the emitter 43 and the collector 45, if desired.

Another suitable target member embodiment is that shown in FIG. 3 in which the target member 55 includes an NP'N transistor having an N-type emitter 59, a P-type base region 61 and an N-type collector 57. Also shown are a transition region in the form of a base-emitter PN junction 65, and another transition region in the form of a collector-base PN junction 63. As can be seen in FIG. 3, the base region curves toward the surface, and when it approaches the surface of the transistor, the emitter-base PN junction 65 and the collector-base PN junction 63 are substantially parallel to the impinging electron beam 15.

With the target members 19 and 55, shown in FIGS. 1 and 3, respectively, the electron beam 15 is focused in such a way that when zero-AC. voltage is applied to the deflection plates 17, the electron beam is in complete contact with the base regions 25 and 61, respectively. As an AC. voltage is applied to the deflection plates 17, the electron beam 15 is swept across the base regions 25 and 61 and contacts the interceptor 33 or the emitter region 21 or 59, respectively, or if an interceptor is not utilized, the electron beam may contact the collector 23 or 57. The electron beam 15 is effective in changing the impedance characteristics of the target members only during the period when the beam is in contact with the base region. The efiect of these electrons being injected into the base region is to radically change the impedance of the target member.

It is, of course, understood that the particular embodiments of the target members shown in FIGS. 1, 2 and 3 are only a few of the many physical arrangements that are suitable, and that various types of transistors can be used as the ultimate target as mentioned previously. However, :all embodiments have the advantage of the increased current multiplication due to both pair production and transistor current multiplication. Also, it should be noted that my invention is unique in combining a very high input impedance with an extremely low output impedance beyond the magnitude of either electron tubes or transistors.

The extremely high transductance and current multiplication, which may be obtained, indicate that a signal converter may be made utilizing the above principles which will provide an intermediate frequency signal level on the order of 1 volt when an input signal on the order of a fraction of a microvolt is applied. At the same time, a control grid can be used to perform the oscillator function for the signal conversion within the same tube. Tubes utilizing the principles of my invention can be used as signal converters, oscillator tuning elements, intermediate frequency amplifiers, mixers and other uses with the corresponding reduction, not only in the number of components needed, but also in current consumption.

In general, a junction should be provided in close proxmity to the emitter connection in order to provide adequate sensitivity and heat dissipation. Also, good ther mal connection should be made to as many parts of the target as possible in order to provide satisfactory heat dissipation. In addition, adequate provision must be made for heat radiation for the semiconductor assembly, such as by the provision of metallic cooling fins or members having good thermal radiation characteristics. These cooling members may be blackened, if desired, to provide better heat radiation.

While the present invention has been shown in a few forms only, it will be obvious to those skilled in the art that it is'not so limited but is susceptible of various changes and modifications without departing from the spirit and scope thereof. 7

I claim as my invention:

1. An electron beamdevice including an envelope, a generating means for generating an electron beam, a target member, deflecting means for deflecting said electron beam over said transistor target member so that the current from said transistor target member is continuously variable in response to signals applied to said deflecting means, said transistor target member including a first zone of semiconductor material, a second zone of semiconductor material, and a third zone of semiconductor material positioned between said first zone and second zone, a semiconductor transition region between said first zone and said third zone and a semiconductor transition region between said second zone and said third zone, said third zone being of a different conductivity type from said first zone and from said second zone a fixed electrical contact on said first zone, a fixed electrical contact on said second zone, and said electron beam operable to provide the sole electrical contact to said third zone.

2. An electron beam device including an envelope, a target member, a generating means for generating an electron beam, deflecting means for deflecting said electron beam over said target member so that the current from said target member is continuously and linearly variable in response to signals applied to said deflecting means, said target member including a first zone of semiconductor material, a second zone of semiconductor material, and a third zone of semiconductor material positioned between said first zone and second zone, a semiconductor transition region bet-ween said first zone and said third zone and a semiconductor transition region between said second zone and said third zone, said third zone being of a different conductivity type from said first zone and from said second zone, said semiconductor transition regions being substantially parallel to the axis of said electron beam when said electron beam is inan undefiected condition and being exposed to direct incidence of said electron beam in one or more positions of said beam as determined by said deflecting means, a fixed electrical contact on said first zone, a fixed electrical contact on said second zone, and said electron beam operable to provide the sole electrical contact to said third zone.

1 3. An electron beam device including an envelope, a generating means for generating an electron beam, a target member, deflecting means for deflecting said electron beam over said target member so that the current from said target member is continuously and linearly variable in response to signals applied to said deflecting means, said target member including a semiconductor collector of a first conductivity type, a semiconductor emitter of the same type conductivity as said collector, and a semiconductor base region of conductivity type opposite to that of said collector disposed between said collector and said emitter, a PN junction between said collector and said base region, a PN junction between said emitter and said base region, said PN junctions being substantially perpendicular to the axis of said electron beam when said electron beam is in an undeflected condition, said emitter having an aperture therein, a fixed electrical contact to said collector, a fixed electrical contact to said emitter, and said electron beam being operable to provide the sole electrical contact to said base region through said emitter aperture.

4. An electron beam device including an envelope, a generating means for generating an electron beam, deflecting means for deflecting said electron beam and a target member comprising a transistor including an emitter, a collector and a base region between said emitter and said collector, said deflecting means being operable to cause said electron beam to strike said base region of said transistor when undeflected and to strike other predetermined portions of said target member upon deflection to provide a continuously and linearly variable output signal from said target member being a maximum when said beam is wholly incident on said base region and being substantially zero when said beam is Wholly incident more than a diffusion length from said base region, a fixed electrical contact on said emitter region, a fixed electrical contact on said collector region, and said electron beam operable to provide the sole electrical contact to said base region.

5. An electron beam device comprising an electron beam source, a target and deflecting means for deflecting an electron beam from said electron beam source into incidence with predetermined portions of said target, said target comprising a junction-type transistor having an emitter, a collector and a base region, said base region separated by a first PN junction from said emitter and by a second PN junction from said collector, said first and second PN junctions separated by a distance of about 0.001 mm. to about 0.01 mm., said deflecting means being operable to cause said electron beam to strike said base region close to said PN junctions when in one or more positions w determined by said deflecting means to provide a continuously and linearly variable output signal from said target member being a maximum when said beam is wholly incident on said base region and being substantially zero when said beam is wholly incident more than a diffusion length from said base region, a fixed electrical contact on said emitter region, a fixed electrical contact on said collector region, and said electron beam operable to provide the sole electrical contact to said base region.

References Cited in the file of this patent UNITED STATES PATENTS 2,524,033 Bardeen Oct. 3, 1950 2,547,386 Gray Apr. 3, 1951 2,641,712 Kircher June 9, 1953 2,641,713 Snive June 9, 1953 2,691,076 Moore et a1. Oct. 5, 1954 2,803,779 Rittner et a1 Aug. 20, 1957 2,860,282 Hansen Nov. 11, 1958 2,867,732 Rutz Jan. 6, 1959 2,867,733 Hunter Jan. 6, 1959 2,886,739 Matthews et a1. May 12, 1959 FOREIGN PATENTS 692,337 Great Britain June 3, 1953 

